Additive for improving the thermal stability of hydrocarbon compositions

ABSTRACT

The invention relates to the use of at least one additive in order to increase the thermal stability of a hydrocarbon composition, said additive being the product of the condensation reaction between at least one alkenyl succinic or alkyl succinic anhydride I and a primary amine II. The invention also relates to a composition comprising the aforementioned additive, an anti-oxidant and a metal deactivator and to fuels containing same.

A subject of the invention is the use of an additive for improving thethermal stability of hydrocarbon compositions, as well as a particularhydrocarbon composition having an improved thermal stability.

Fuels intended to function in aeroplane engines (for example turbojetengines and ramjet engines), usually called kerosene or jet fuel, areknown. They are generally composed of a middle cut from crude oildistillation, generally containing additives.

In an aeroplane, the fuel, in addition to its role of propellant fluid,fulfils other functions. These functions are in particular:

-   -   coolant fluid by means of exchangers: fuel/hydraulic fluid        (cooling the hydraulic fluid); fuel/oil (cooling the lubrication        oil); fuel/air (cooling the fuel);    -   power-transmission fluid: nozzle actuators    -   regulation fluid (in particular for the engine).

Until its injection into the combustion chamber or the afterburner, thefuel can be subjected to high temperatures, for example of the order of200° C., or even higher in contact with the walls.

Subjected to these high temperatures, the fuel is subject to oxidationand thermal decomposition phenomena which cause the formation ofvarnishes and gums on the one hand, and particles and coke on the other.When deposited on fittings which constitute the fuel system of anaeroplane, these products cause damage and malfunctions (in particularmalfunction of the main injectors, damage to the combustion chambers,and to the first turbine stage (excessive temperature), malfunction ofthe afterburner injectors, vibrations, loss of efficiency of the heatexchangers, etc.) Starting problems (in particular from cold), in-flightreignition, loss of performance can thus occur. These problems alsosignificantly increase the maintenance costs of aeroplanes. Moreover,new generation aeroplanes present still further problems or accentuatethe existing problems as they aim to increase the thrust/weight ratio ofthe engine and to reduce the fuel consumption, which involves: anincrease in the speed of rotation of the engine and consequently anincrease in the operating temperature of the engine and of thelubrication oil; a reduction in the size of the exchangers (dimensions,weight); an increase in the number of electric and electronic circuitsto be cooled and a reduction in the fuel feed rate (consumption). Thistherefore requires an increase in the thermal capacity of the fuel whichmust be capable of removing a greater quantity of heat.

It is therefore sought to improve the thermal stability of the fuel byincorporation of an additive or a composition of additives capable ofresponding to the demands of future aeroplanes and reducing themaintenance costs while responding to the technical problems mentionedabove. The increase sought is of at least 100° F., i.e. allowing anincrease from 325° F. (163° C.) to 425° F. (218° C.) for the maximumtemperatures currently encountered and an increase from 400° F. (204°C.) to 500° F. (259° C.) for the temperatures of the fuel in contactwith the walls.

To solve these problems, U.S. Pat. No. 5,468,262 describes an additivefor improving the thermal stability of a fuel, this additive beingprepared by (i) reaction of a polyamine, an aldehyde and a phenol toform a phenol-aldehyde-amine condensate; and (ii) Mannich's reaction ofthis condensate with a succinic anhydride carrying a substituent whichis a polyolefin with residual unsaturation, in particular polyisobutene.This additive can be schematically represented by the following formula(with PIB for polyisobutene and PA for polyamine/aldehyde):

This additive is used, according to this document, in a proportioncomprised between 0.2 and 20% by weight of fuel. Such an additive posesseveral specific problems. Firstly, the quantities required for theadditive to be effective are very large, such that they exceed 2000 ppm,which makes the end fuel very expensive. Moreover, the presence of aheavy PIB group (with residual unsaturation) encourages the initiationof deposits on the walls, which is exactly what one wants to avoid.Finally, such an additive is surface-active by nature(hydrophobic/hydrophilic duality) and significant levels of it encouragecontamination of fuel by water, which should be avoided, in particularin fuels for aeroplanes.

EP-A-0678568 describes an additive reducing the deposits in aeroplanejet engines. This additive is a derivative of (thio)-phosphonic acid,used in the example in a quantity of 25 ppm. It is preferably aderivative of polyisobutene thiophosphonic acid, more particularly itsester with pentaerythritol.

However, this additive poses several problems. On the one hand, it isphosphorus-based, which causes atmospheric pollution linked to thedischarge of acid compounds (phosphates, phosphoric acids) in thecombustion gas. On the other hand, it also comprises a polyisobutenegroup, and thus poses the same problems as those already outlined abovefor the additive which is the subject-matter of U.S. Pat. No. 5,468,262.

In order to solve the problems of thermal decomposition and oxidation ofthe hydrocarbon flow subjected to high temperatures in heat exchangersin refineries, U.S. Pat. No. 3,437,583 proposes the incorporation intothe flow of hydrocarbons of an anti-fouling composition comprising ahindered phenol, a succinimide obtained by reaction of an acid orsuccinic anhydride substituted by a polyamine, andN,N′-disalicylidene-1,2-propane diamine.

The succinimide is obtained from an anhydride or a succinic acidsubstituted by an R′″ radical comprising 30 to 200 carbon atoms. Thereagain, the presence of such a heavy group encourages the thermaldecomposition of the additive, and ultimately proves to be a precursorof deposits and fouling.

U.S. Pat. No. 3,776,835 also describes a method of reducing the rate offouling on the inside of heat exchangers in which the hydrocarbon flowcirculates. This method consists of adding to the hydrocarbon flow (a)hydrogen and (b) an agent for inhibiting deposits, chosen from mono- andpoly-amines and -amides comprising 50 carbon atoms. Among the familiesof chemical compounds capable of being used as agents for inhibitingdeposits there are generally mentioned succinimides comprising 20 to 200carbon atoms.

The use of succinimide-based additives in hydro-carbonated fuels ismoreover known to improve other types of properties, in particular coldproperties.

Thus Patent Application EP 626.442 deals with problems of degradation ofthe cold resistance caused by using ester fuels produced from thetransesterification of animal or vegetable oils or fats, and recommendsthe use of such esters combined with a pour point depressant additiveand optionally a carboxylic dispersant which can be, among others, acompound obtained by reaction of a substituted succinic anhydride withan amine.

Long-chain succinimides are largely preferred: the succinic acidsubstituent contains a minimum of 12 and preferably 50 carbon atoms,with a very clear preference for polymers of molecular weight rangingfrom 700 to 10,000.

The succinimide-based additives are used here as dispersant agents incold-resistance compositions. In other words their function is toimprove still further the cold resistance of the mixture by keeping insuspension the hydrocarbon crystals which form at low temperature toprevent them being deposited. This antisedimentation function relatesonly to the properties of low-temperature fuels, and makes nocontribution to thermal stability at high temperature.

Similarly, U.S. Pat. No. 3,795,495 recommends the use of succinimidescombined with an alkyl aminoalkyl phosphate to solve the cold-startingproblems of petrol vehicles in the case of the fuel freezing.Succinimide is the product of condensation of a succinic anhydridecarrying a substituent R comprising 8 to 50 carbon atoms with apolyamine. There again, the succinimides are used as anti-freezingagents, which implies nothing about their effectiveness as thermalstability additives at high temperature.

A subject of the invention is an additive which allows the thermalstability of the hydrocarbon compositions, in particular fuels foraeroplanes, to be improved with a greater effectiveness than additivesalready known for this while avoiding the problems encountered withthese additives.

The present invention therefore proposes the use, to increase thethermal stability of a hydrocarbon composition, of at least one additivewhich is the product of the condensation reaction between:

-   -   (i) at least one alkylsuccinic or alkenylsuccinic I anhydride of        general formula(I):        in which:    -   R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms;        and    -   (ii) at least one primary amine II of general formula (II):        NH₂—[(CH₂)_(m)—(CHR₁)_(n)-Z]_(x)-[(CH₂)_(p)—(CHR₂)_(q)]_(y)—NHR₃        -   in which:        -   R₁ and R₂ are chosen from hydrogen, alkyl groups comprising            1 to 30 carbon atoms, phenyl groups,        -   R₃ is hydrogen or an alkyl group comprising 1 to 30 carbon            atoms or a phenyl group or an alkylaromatic group,        -   Z is oxygen or the NH group,        -   x is an integer from 0 to 5 inclusive,        -   y is an integer from 1 to 5 inclusive,        -   m, n, p and q are integers from 0 to 10 inclusive.

The invention also proposes a composition of additives which allows thethermal stability of hydrocarbons to be improved. This compositioncomprises:

-   -   (a) 1 to 40 parts by weight of at least one antioxidant;    -   (b) 0.05 to 10 parts by weight of at least one metal        deactivation agent; and    -   (c) 1 to 60 parts by weight of at least one thermal stability        additive which is the product of the condensation reaction as        described above.

It has been noted surprisingly that the combination of the threeconstituents (a), (b) and (c) above, if these constituents are presentin the relative proportions mentioned above, allows the thermalstability of the hydrocarbon compositions to be significantly improved.In particular, the abovementioned composition allows the thermalbreakpoint of fuels intended for aviation to be greatly increased, whichallows these fuels to be used as coolant fluids at higher temperaturesor, at the same temperature, the thermal decomposition of the fuel to besignificantly reduced in the heat exchange zones.

The invention also provides a hydrocarbon composition comprising a majorpart of a hydrocarbon mixture and the composition of additives above, ina quantity such that the concentration of said composition as thermalstability additive ranges from 1 to 200 ppm, preferably 1 to 100 ppm,advantageously 1 to 50 ppm.

In the present specification, all concentrations expressed in ppm (partsper million) designate ppm by weight.

The invention also provides a stock solution comprising a solvent andthe composition of additives above.

The invention also provides a process for the preparation of thecomposition of additives above, by mixing different constituents.

The invention finally provides a method for increasing the thermalstability of fuels for aeroplanes, by incorporating an additive or acomposition of additives as described above into said fuels.

The invention will now be described in more detail in the descriptionwhich follows.

The term “alkyl” applies to linear and branched groups.

By the term “alkylaromatic” is meant groups having an alkyl chain whichcarries an aromatic distal substituent, in particular a phenyl group,the alkyl chain having 1 to 30 carbon atoms.

The term “hydrocarbon mixture” designates any hydrocarbon mixturecapable of being used as fuel. The hydrocarbon mixture is advantageouslychosen from gasolines, gasoils, kerosenes, DFOs (Domestic Fuel Oil),heavy fuels, synthesis hydrocarbons such as those obtained byoligomerization of olefins or by Fischer-Tropsch synthesis, biofuelssuch as vegetable oils and the esters of vegetable oils, and mixtures ofthese products.

The hydrocarbon mixture preferably comprises a middle distillate, i.e. acut of hydrocarbons the distillation range (determined according to theASTM D 86 standard) of which is comprised between 60 and 350° C.,preferably between 100 and 300° C.

Advantageously, this composition is an aeroplane fuel, for examplekerosene, alone or mixed with a gasoline. There may be mentioned forexample the fuels known to a person skilled in the art under thefollowing names: JP-4, (MIL-T-5624), JP-5, JP-7, JP-8 (MIL-T-83133), JetA and JetA-1 (ASTM D 1655). Kerosene can have a distillation rangecomprised in the range from 60° C. to 360° C., and for example astarting point of 149-221° C., 50% point of 221-231° C., 90% point of260-343° C. Its API gravity can be 30 to 40. For more details, referencecan be made to the publication “Handbook of Aviation Fuel Properties”,Coordinating Research Council Inc., CRC Report No. 530 (SAE, Warrendale,USA, 1983). Particularly advantageous aeroplane fuels are those whichconform to the AFQRJOS specification (“Aviation Fuel QualityRequirements for Jointly Operated Systems”) Issue 18 for Jet A-1 ofNovember 1999 (this specification reiterates the most restrictivecriteria of the ASTM D 1655 specification and the British DEF STAN 91-91specification).

The hydrocarbon mixture can have been partly or wholly subject to adesulphuration and/or denitrogenation and/or dearomatization treatment.For example, fuels that have been hydrotreated can be used under more orless severe conditions (comprising a hydrodesulphuration, a saturationof the aromatic and olefinic compounds, even a hydro-denitrogenation).

The hydrocarbon composition advantageously has a sulphur content lessthan or equal to 0.5% by weight, preferably less than or equal to 0.3%by weight. Its content of aromatic compounds is preferably less than orequal to 25% by volume. It can optionally contain a substantial quantityof oxygenated compounds such as ethers, and/or biofuels such asalcohols, or esters of fatty acids such as for example the methyl esterof rape seed.

Other hydrocarbon compositions are also suitable; the fuel can beintended for applications not related to engines, for example a fuel forovens, boilers or fuel cells.

The additive according to the invention, as well as the composition ofadditives, allows the thermal stabilization of the hydrocarboncomposition, and therefore responds to the technical problems outlinedabove. The additive according to the invention is generally used in aquantity of 1 to 200 ppm, preferably 1 to 100 ppm, advantageously 1 to50 ppm.

The additive according to the invention is prepared by reacting ananhydride I with an amine II. This reaction is carried out at atemperature for example of between 120 to 200° C., and for a period forexample between 1 and 36 hours and preferably between 5 and 30 hours.

Condensation of the amines II with the anhydrides I can be carried outwithout solvent, but a hydrocarbon solvent with a boiling point between70 and 250° C. is preferably used. The solvent preferably comprises anaromatic or naphthenoaromatic hydrocarbon, for example: toluene,xylenes, diisopropylbenzene or also a petroleum cut with a suitabledistillation range.

The additives considered in the invention can in practice be prepared inthe following manner: amine II is gradually introduced into a reactorcontaining anhydride I, maintaining the temperature between 30° C. and80°. The temperature is then increased to a value of 120 to 200° C., thevolatile products formed (in particular water) being eliminated eitherby entrainment with a stream of inert gas or by azeotropic distillationwith the chosen solvent; the final concentration of dry material is forexample 40 to 70%.

The preparation methods disclosed for example in the applicationWO-A-9413758, to which reference is made and the content of which isincorporated into the present application, can be generally applied.

For the preparation of the additive according to the invention, ananhydride I in which the side chain R comprises 4 to 24 carbon atoms,even more preferably 12 to 24 carbon atoms, is preferably used. The sidechain R is preferably an alkenyl group.

Examples of alkylsuccinic and alkenylsuccinic anhydride aredodecylsuccinic, dodecenylsuccinic, hexadecylsuccinic,hexadecenylsuccinic, octadecylsuccinic, octadecenylsuccinic,eicosylsuccinic and eicosenylsuccinic anhydrides.

In the additive according to the invention, the amine corresponds toformula II. The R₁ and R₂ groups are preferably either hydrogen or alkylgroups comprising 1 to 10 carbon atoms, and/or R₃ is hydrogen or analkyl group comprising 1 to 20 carbon atoms, and/or Z is the NH group,and/or m, n, p and q are comprised between 1 and 3 inclusive. Theindices x and y are preferably comprised between 0 and 2 inclusive.

Advantageously, amine II corresponds to the following formula IIa:NH₂—[(CH₂)_(m)—NH]_(x)—[(CH₂)_(p+1)]_(y)—NH₂.

Non-limitative examples of such amines are: for non-alkylated amines:

-   -   diethylenetriamine, dipropylenetriamine,    -   triethylenetetramine, tetraethylenepentamine and    -   tetrapropylenepentamine;        and for alkylated amines:    -   N-alkylethylenediamines, N-alkylpropylenediamines,    -   N-alkylbutylenediamines, N-alkyldiethylenetriamines,    -   N-alkyldipropylenetriamines, N-alkyldibutylenetriamines,    -   N-alkyltriethylenetetramines, N-alkyltributylenetetramines    -   and N-alkyltripropylenetetramines        having an alkyl radical comprising 1 to 10 carbon atoms.

For the preparation of the additive, the anhydride I and the amine IIare used in a preferential molar ratio of anhydride:amine comprisedbetween 1:0.2 and 1:1.

The molecular mass by weight of the additive can vary between 300 and10000 g/mol.

It is particularly advantageous to use the additive described above incombination with an antioxidant, in a quantity relative to thehydrocarbon composition for example comprised between 1 and 1000 ppm,preferably between 1 and 100 ppm. Sterically hindered phenols can beused as antioxidants such as:

-   -   2,6-di-t-butyl-4-methylphenol (BHT),    -   2,6-di-t-butylphenol,    -   4,4′-methylene bis(2,6-di-t-butyl-phenol),    -   2,6-di-t-butyl-4-dimethylaminomethylphenol,    -   2,4,6-tri-t-butylphenol and    -   2,4-di-methyl-6-t-butylphenol.

It is likewise advantageous to use a metal deactivation agent in aquantity relative to the hydrocarbon composition for example comprisedbetween 0.1 and 500 ppm, preferably between 0.1 and 20 ppm. Metalchelating compounds can be used as deactivation agents such as forexample N,N′-disalicylidene-1,2-propane diamine of formula:

Thus, the hydrocarbon composition according to the inventionadvantageously comprises:

-   -   (a) 1 to 1000 ppm, and preferably 1 to 100 ppm of at least one        antioxidant;    -   (b) 0.1 to 500 ppm, preferably 0.1 to 20 ppm of at least one        metal deactivation agent;    -   (c) 1 to 200 ppm, preferably 1 to 100 ppm, advantageously 1 to        50 ppm of the thermal stability additive according to the        invention.

It can also advantageously comprise other additives chosen from theadditives usually used for the applications considered, namely forexample corrosion-inhibiting additives, anti-freeze additives,antistatic additives, additives improving the cold properties, traceradditives, detergent additives, and their mixtures. The hydrocarboncomposition preferably contains at least one detergent additive chosenfrom the polyisobuteneamines.

In particularly advantageous manner, the composition of additivesaccording to the invention comprises:

-   -   (a) 2 to 40 parts by weight and preferably 4 to 15 parts by        weight of at least one antioxidant;    -   (b) 0.1 to 3 parts by weight and preferably 0.5 to 2 parts by        weight of at least one metal deactivation agent; and    -   (c) 2 to 20 parts by weight and preferably 3 to 15 parts by        weight of at least one thermal stability additive as described        above.

With these ranges of proportions relative to the three constituents (a),(b) and (c), the effectiveness of the composition of additives isparticularly significant, and the increase in thermal stability isconsiderably improved.

In general the additive is supplied in the form of a concentratedsolution (“stock solution”) either of thermal stability additive aloneor of the composition of additives (a), (b) and (c), or the thermalstability additive mixed with any other standard additive. These “stocksolutions” are prepared by dissolving additives in a solvent which canbe chosen from the aromatic solvents mentioned above, petroleum cuts (inparticular kerosenes), mineral and/or synthesis oils. The “stocksolutions” can contain for example 20 to 60% by weight additives andagents. According to its concentration, the stock solution is introducedinto the hydrocarbon composition in quantities which can range forexample from 150 ppm weight to 1000 ppm weight.

The following examples illustrate the invention without limiting thescope.

Two additives A and B according to the invention are prepared, each bycondensation of an anhydride I of formula (I) with a primary amine II offormula (II). Table 1 below details the formula of each of the reagentsI and II: TABLE 1 Addi- Formula tive R Z R₃ x y m n and q p A C₂₄ NH H 11 2 0 1 alkenyl group B C₁₈ NH Mixture of C₁₄ to 2 0 3 0 1 alkenyl C₁₈alkyl groups group

These additives were prepared in the following manner:

Additive A:

a) Synthesis of the Anhydride I:

246.8 g of linear C₂₄ alpha-olefin are heated in a reactor to 185° C.under nitrogen and under stirring. 91.1 g of maleic anhydride are thenadded at a rate such the temperature of the reaction medium remains at185° C.±2.5° C. The reaction mixture is stirred for 24 hours at 185° C.,then cooled down to 60° C. by adding 500 g of xylene (solvent).

b) Synthesis of the Additive:

161.5 g of diethylenetriamine (DETA) are added to the mixture from stage(a), maintaining the temperature at approximately 60° C. Then the waterwhich forms during the condensation reaction is eliminated together withpart of the solvent, by azeotropic distillation, with a startingdistillation temperature of at least 90° C., and a final distillationtemperature of approximately 150° C.

The mixture is then cooled down and filtered, and the condensationproduct is thus recovered in solution in xylene.

Additive B:

a) Synthesis of the Anhydride I:

234.3 g of linear C₁₈ alpha-olefin (n-octadecene) are heated to 185° C.in a reactor under nitrogen and under stirring. 91.1 g of maleicanhydride are then added at a rate such that the temperature of thereaction medium remains at 185° C.±2.5° C. The reaction mixture isstirred for 24 hours at 185° C., then cooled down to 60° C. by adding500 g of xylene (solvent).

b) Synthesis of the Additive:

190.6 g of tallow triamine are added to the mixture from stage (a),maintaining the temperature at approximately 60° C. Then the water whichforms during the condensation reaction is eliminated together with partof the solvent, by azeotropic distillation, with a starting distillationtemperature of at least 90° C., and a final distillation temperature ofapproximately 150° C.

The mixture is then cooled down and filtered, and the condensationproduct is thus recovered in solution in xylene.

These additives were tested in two JetA-1-type aviation fuels, theproperties of which are given in Table 2 below: TABLE 2 Jet no. 1 Jetno. 2 Kerosene cut treated Hydrotreated in a non-extractive Typekerosene cut Kerox unit Sulphur content 0.0003% by weight 0.0166% byweight Initial distillation point 145.4° C. 152.9° C. 10% distillationpoint 161.4° C. 176.1° C. 50% distillation point 189.7° C. 202.0° C. 90%distillation point 238.4° C. 235.5° C. Final distillation point 257.5°C. 249.8° C. Density at 15° C. 816.7 kg/m³ 808.0 kg/m³

The sulphur content was determined in accordance with the ASTM D 1266standard, the distillation points in accordance with the ASTM D 86standard and the density in accordance with the ASTM D 1298 standard.

The non-extractive Kerox process converts the mercaptans contained in apetroleum cut to disulphides.

These two fuels comply with the AFQRJOS specification (“Aviation FuelQuality Requirements for Jointly Operated Systems”) Issue 18 for Jet A-1of November 1999. This specification reiterates the most restrictivecriteria of the ASTM D 1655 specification and the British DEF STAN 91-91specification.

The additives were incorporated into the two fuels mixed with anantioxidant (2,6-di-t-butylphenol) and a metal deactivation agent(N,N′-disalicylidene-1,2-propane diamine) The thermal stabilitybreakpoint (here called “breakpoint”) of each of the fuels before andafter the addition of additives was determined in accordance withparagraph X2 of the ASTM D 3241 standard.

The breakpoints of the fuels to which additives have not been added areas follows:

-   -   Jet no. 1 295° C.    -   Jet no. 2 305° C.

Tables 3 and 4 below detail the composition of the fuels to whichadditives have been added and the results obtained, with additives A andB respectively. TABLE 3 (ADDITIVE A) Fuel Jet no. 1 Jet no. 2 Content ofA  25 ppm  25 ppm Content of antioxidant  20 ppm  20 ppm Content ofmetal deactivator 2.5 ppm 2.5 ppm Breakpoint 335° C. 335° C.

TABLE 4 (ADDITIVE B) Fuel Jet no. 1 Jet no. 2 Jet no. 2 Content of B  25ppm   8 ppm  25 ppm Content of antioxidant  20 ppm  20 ppm  20 ppmContent of metal deactivator 2.5 ppm 2.5 ppm 2.5 ppm Breakpoint >400° C.345° C. 345° C.

Tables 3 and 4 above illustrate the excellent performances of additivesaccording to the invention in terms of improving the thermal stabilityof aviation fuels. In fact, additives A and B generally allow anincrease of at least 30° C. in the thermal stability breakpoint. Theincrease is often greater, and in the case of additive B it can even beof the order of 100° C.

This increase has been confirmed on very different jet fuels, whichdemonstrates the effectiveness of the additives regardless of the fuel.

1-29. (canceled)
 30. Use to increase the thermal stability of ahydrocarbon composition, of at least one additive which is the productof the condensation reaction between: (i) at least one alkylsuccinic oralkenylsuccinic anhydride I of general formula(I):

in which: R is an alkyl or alkenyl group comprising 4 to 29 carbonatoms; and (ii) at least one primary amine II of general formulaNH₂—[(CH₂)_(m)—(CHR₁)_(n)-Z]_(x)-[(CH₂)_(p)—(CHR₂)_(q)]_(y)—NHR₃   (II)in which: R₁ and R₂ are chosen from hydrogen, alkyl groups comprising 1to 30 carbon atoms, phenyl groups, R₃ is hydrogen or an alkyl groupcomprising 1 to 30 carbon atoms or a phenyl group or an alkylaromaticgroup, Z is oxygen or the NH group, x is an integer from 0 to 5inclusive, y is an integer from 1 to 5 inclusive, m, n, p and q areintegers from 0 to 10 inclusive.
 31. Use according to claim 30, inwhich, in the additive, the formula of the amine of formula II isNH₂—[(CH₂)_(m)—NH]_(x)—[(CH₂)_(p+1)]_(y)—NH₂.
 32. Use according to claim30, in which the additive is the product of the condensation reactionbetween compounds I and II, used according to molar ratio I:II comprisedbetween 1:0.2 and 1:1.
 33. Use according to claim 30, in which in theadditive, the side chain R is an alkyl or alkenyl group comprising 4 to24 carbon atoms.
 34. Use according to claim 33, in which the side chainR comprises 12 to 24 carbon atoms.
 35. Use according to claims 30, inwhich in the additive, the side chain R is an alkenyl group.
 36. Useaccording to claim 30, in which in the additive, the R₁ and R₂ groupsare either hydrogen or alkyl groups comprising 1 to 10 carbon atoms. 37.Use according to claim 30, in which in the additive, R₃ is hydrogen oran alkyl group comprising 1 to 20 carbon atoms.
 38. Use according toclaim 30, in which in the additive, Z is the NH group.
 39. Use accordingto claims 30, in which in the additive, m, n, p and q are comprisedbetween 1 and 3 inclusive.
 40. Use according to claim 30, in which theadditive is used at the rate of 1 to 200 ppm.
 41. Use according to claim30, in which the additive is used at the rate of 1 to 100 ppm.
 42. Useaccording to claim 30, in which the additive is used at the rate of 1 to50 ppm.
 43. Use according to claims 30, in which the additive is used incombination with an antioxidant and a metal deactivation agent. 44.Method of increasing the thermal stability of aviation fuels comprisingthe incorporation into said fuels of an additives as describe in claim30.
 45. Composition comprising: (a) 1 to 40 parts by weight of at leastone antioxidant; (b) 0.05 to 10 parts by weight of at least one metaldeactivation agent; and (c) 1 to 60 parts by weight of at least onethermal stability additive which is the product of the condensationreaction between: (i) at least one alkylsuccinic or alkenylsuccinicanhydride I of

general formula(I): in which: R is an alkyl or alkenyl group comprising4 to 29 carbon atoms; and (ii) at least one primary II amine of generalformula (II):NH₂—[(CH₂)_(m)—(CHR₁)_(n)-Z]_(x)-[(CH₂)_(p)—(CHR₂)_(q)]_(y)—NHR₃ inwhich: R₁ and R₂ are chosen from hydrogen, alkyl groups comprising 1 to30 carbon atoms, phenyl groups, R₃ is hydrogen or an alkyl groupcomprising 1 to 30 carbon atoms or a phenyl group or an alkylaromaticgroup, Z is oxygen or the NH group, x is an integer from 0 to 5inclusive, y is an integer from 1 to 5 inclusive, m, n, p and q areintegers from 0 to 10 inclusive.
 46. Composition according to claim 45,comprising (a) 2 to 40 parts by weight of antioxidant; (b) 0.1 to 3parts by weight of metal deactivation agent; and (c) 2 to 20 parts byweight of thermal stability additive.
 47. Composition according to claim45, in which the antioxidant is a sterically hindered phenol. 48.Composition according to claims 45, in which the metal deactivationagent is a metal chelating agent.
 49. Hydrocarbon composition comprisinga major part of a hydrocarbon mixture and the composition according toclaim 45, in a quantity such that the concentration in said compositionof thermal stability additive is 1 to 200 ppm.
 50. Hydrocarboncomposition comprising a major part of a hydrocarbon mixture and thecomposition according to claim 45, in a quantity such that theconcentration in said composition of thermal stability additive is 1 to100 ppm.
 51. Hydrocarbon composition comprising a major part of ahydrocarbon mixture and the composition according to claim 45, in aquantity such that the concentration in said composition of thermalstability additive is 1 to 50 ppm.
 52. Stock solution comprising asolvent and the composition according to claim
 45. 53. Stock solutionaccording to claim 45, in which the solvent is chosen from aromaticsolvents, petroleum cuts, in particular kerosenes, mineral and/orsynthesis oils.
 54. Process for the preparation of a compositionaccording to claim 45, by mixing various constituents.
 55. Method ofincreasing the thermal stability of aviation fuels comprising theincorporation into said fuels of a composition of additives according toclaim
 45. 56. Composition comprising: (a) 1 to 40 parts by weight of atleast one antioxidant; (b) 0.05 to 10 parts by weight of at least onemetal deactivation agent; and (c) 1 to 60 parts by weight of at leastone thermal stability additive which is the product of the condensationreaction between: (i) at least one alkylsuccinic or alkenylsuccinicanhydride I of general formula(I):

in which: R is an alkyl or alkenyl group comprising 4 to 29 carbonatoms; and (ii) at least one primary II amine of general formula(II):NH₂—[(CH₂)_(m)—NH]_(x)—[(CH₂)_(p+1)]_(y)—NH₂. in which: x is an integerfrom 0 to 5 inclusive, y is an integer from 1 to 5 inclusive, m, p areintegers from 0 to 10 inclusive.
 57. Composition according to claim 56,comprising (a) 2 to 40 parts by weight of antioxidant; (b) 0.1 to 3parts by weight of metal deactivation agent; and (c) 2 to 20 parts byweight of thermal stability additive
 58. Composition according to claim56, in which the antioxidant is a sterically hindered phenol. 59.Composition according to claims 56, in which the metal deactivationagent is a metal chelating agent.
 60. Hydrocarbon composition comprisinga major part of a hydrocarbon mixture and the composition according toclaim 56, in a quantity such that the concentration in said compositionof thermal stability additive is 1 to 200 ppm.
 61. Hydrocarboncomposition comprising a major part of a hydrocarbon mixture and thecomposition according to claim 56, in a quantity such that theconcentration in said composition of thermal stability additive is 1 to100 ppm.
 62. Hydrocarbon composition comprising a major part of ahydrocarbon mixture and the composition according to claim 56, in aquantity such that the concentration in said composition of thermalstability additive is 1 to 50 ppm.
 63. Stock solution comprising asolvent and the composition according to claim
 56. 64. Stock solutionaccording to claim 63, in which the solvent is chosen from aromaticsolvents, petroleum cuts, in particular kerosenes, mineral and/orsynthesis oils.
 65. Process for the preparation of a compositionaccording to claim 56, by mixing various constituents.
 66. Method ofincreasing the thermal stability of aviation fuels comprising theincorporation into said fuels of a composition of additives according toclaim
 56. 67. Hydrocarbon composition comprising a major part of ahydrocarbon mixture and: (a) 1 to 1000 ppm, of at least one antioxidant;(b) 0.1 to 500 ppm, of at least one metal deactivation agent; and (c) 1to 200 ppm, of at least one thermal stability additive which is theproduct of the condensation reaction between: (i) at least onealkylsuccinic or alkenylsuccinic anhydride I of general formula(I):

in which: R is an alkyl or alkenyl group comprising 4 to 29 carbonatoms; and (ii) at least one primary II amine of general formula(II):NH₂—[(CH₂)_(m)—(CHR₁)_(n)-Z]_(x)-[(CH₂)_(p)—(CHR₂)_(q)]_(y)—NHR₃ inwhich: R₁ and R₂ are chosen from hydrogen, alkyl groups comprising 1 to30 carbon atoms, phenyl groups, R₃ is hydrogen or an alkyl groupcomprising 1 to 30 carbon atoms or a phenyl group or an alkylaromaticgroup, Z is oxygen or the NH group, x is an integer from 0 to 5inclusive, y is an integer from 1 to 5 inclusive, m, n, p and q areintegers from 0 to 10 inclusive.
 68. Hydrocarbon composition accordingto claim 67, comprising a major part of a hydrocarbon mixture and: (a) 1to 100 ppm of at least one antioxidant; (b)
 0. 1 to 20 ppm of at leastone metal deactivation agent; and (c) 1 to 100 ppm of at least onethermal stability additive.
 69. Hydrocarbon composition according toclaim 67 comprising 1 to 50 ppm of at least one thermal stabilityadditive.
 70. Hydrocarbon composition according to claim 67, in whichthe antioxidant is a sterically hindered phenol.
 71. Hydrocarboncomposition according to claim 67, in which the metal deactivation agentis a metal chelating agent.
 72. Hydrocarbon composition according toclaim 67, in which the hydrocarbon mixture is chosen from gasolines,gasoils, kerosenes, DFOs (Domestic Fuel Oil), heavy fuels, synthesishydrocarbons such as those obtained by the oligomerization of olefins orby Fischer-Tropsch synthesis, biofuels such as vegetable oils and theesters of vegetable oils, and mixtures of these products. 73.Hydrocarbon composition according to claim 67, in which the hydrocarbonmixture comprises a middle distillate having a distillation rangecomprised between 60 and 350° C., preferably between 100 and 300° C. 74.Hydrocarbon composition according to claim 67, which is a fuel, inparticular for aeroplanes.
 75. Process for the preparation of acomposition according to claim 67, by mixing various constituents. 76.Hydrocarbon composition comprising a major part of a hydrocarbon mixtureand: (a) 1 to 1000 ppm, of at least one antioxidant; (b) 0.1 to 500 ppm,of at least one metal deactivation agent; and (c) 1 to 200 ppm, of atleast one thermal stability additive which is the product of thecondensation reaction between: (i) at least one alkylsuccinic oralkenylsuccinic anhydride I of general formula(I):

in which: R is an alkyl or alkenyl group comprising 4 to 29 carbonatoms; and (ii) at least one primary II amine of general formula(II):NH₂—[(CH₂)_(m)—NH]_(x)—[(CH₂)_(p+1)]_(y)—NH₂. in which: x is an integerfrom 0 to 5 inclusive, y is an integer from 1 to 5 inclusive, m, p areintegers from 0 to 10 inclusive.
 77. Hydrocarbon composition accordingto claim 76, comprising a major part of a hydrocarbon mixture and: (a) 1to 100 ppm of at least one antioxidant; (b) 0.1 to 20 ppm of at leastone metal deactivation agent; and (c) 1 to 100 ppm of at least onethermal stability additive.
 78. Hydrocarbon composition according toclaim 76 comprising 1 to 50 ppm of at least one thermal stabilityadditive.
 79. Hydrocarbon composition according to claim 76, in whichthe antioxidant is a sterically hindered phenol.
 80. Hydrocarboncomposition according to claim 76, in which the metal deactivation agentis a metal chelating agent.
 81. Hydrocarbon composition according toclaim 76, in which the hydrocarbon mixture is chosen from gasolines,gasoils, kerosenes, DFOs (Domestic Fuel Oil), heavy fuels, synthesishydrocarbons such as those obtained by the oligomerization of olefins orby Fischer-Tropsch synthesis, biofuels such as vegetable oils and theesters of vegetable oils, and mixtures of these products. 82.Hydrocarbon composition according to claims 76, in which the hydrocarbonmixture comprises a middle distillate having a distillation rangecomprised between 60 and 350° C., preferably between 100 and 300° C. 83.Hydrocarbon composition according to claim 76, which is a fuel, inparticular for aeroplanes.
 84. Process for the preparation of acomposition according to claim 76, by mixing various constituents.